Metal phosphating composition and process



METAL PHOSPHATING COMPOSITION AND PROCESS John Arthur Sharp, Bel'oeil Station, Quebec, Canada, assignor to Canadian Industries Limited, Montreal, Quebec, Canada, a corporation of Canada No Drawing. Filed July 1, 1960, Ser. No. 40,146 A Claims priority, application Canada July 4, 1959 20 Claims. (Cl. 148-615) This invention relates to a new composition and a new process for producing phosphate coatings on metals, and more particularly to new anhydrous composition and a new process for cleaning and phosphating metals in one step.

Phosphate coatings are widely employed in metal finishing, particularly to render surfaces suitable for painting. In currently used procedures, metal work-pieces are normally first degreased, suitably in an aqueous alkali cleaner or, less usually, in a vapour degreaser containing a chlorinated hydrocarbon solvent. A phosphate coating is then applied by immersion of the pieces in an aqueous phosphating solution, suitably a hot solution of a soluble alkali phosphate together with known accelerators, and the phosphate coating may then be passivated by a solution of chromic acid.

The use of aqueous solutions makes it necessary to rinse the metal pieces thoroughly after each stage and then to dry them, since if the phosphating solution, for example, is allowed to dry on the metal, the subsequent adhesion of paint will be poor. Furthermore, the use of aqueous solutions always involves the risk of corrosion commencing before the metal is entirely dry, and the retention of traces of moisture which can cause blistering of a subsequently applied high bake enamel. In addition standard phosphating systems require large amounts of heat to heat the solutions and to dry the treated panels.

It is an object of this invention to provide a composition and a process for phosphating metals which overcome the disadvantages of the compositions and processes of the prior art. A further object is to provide an anhydrous phosphating composition which is compatible with commonly used degreasing solvents. Additional objects will appear hereinafter.

It has indeed been discovered that appreciable quantities of phosphoric acid can be made soluble in chlorinated hydrocarbons by the presence in the solution of certain polyhydroxy esters, namely monoesters of sorbitan and aliphatic acids containing from 12 to 18 carbon atoms. By sorbitan is meant an anhydride of sorbitol.

The new composition of this invention thus consists essentially of a chlorinated hydrocarbon containing from about 1% to by weight of at least one sorbitan monoester of an aliphatic acid having from 12 to 18 carbon atoms per molecule, and from 1 to 6 moles of phosphoric acid per mole of sorbitan monoester, the term mole meaning one gram molecule based upon the apparent or written molecular formula.

The new phosphating process of the invention comprises essentially coating the surface of a metallic article with the aforesaid substantially anhydrous composition, the composition being applied by any convenient means such as immersion of the article in a bath of the composition or spraying or brushing of the composition onto the article.

Although the composition of this invention is capable of degreasing and phosphating metal articles in one Patented May 30, 1961 step, it is desirable in the case of very dirty articles that the bulk of the grease be removed in an earlier stage in order that the phosphating composition may stay clean. This earlier stage may include a conventional non-aqueous vapour or immersion degreasing stage with the advantage that heat requirements are reduced when heating anhydrous solvents, and complete drying by evaporation of solvent is quicker than with aqueous systems. Furthermore, the complicated rinsing and drying procedure of the processes of the prior art may be dispensed with since the phosphating solution of this invention may readily be removed from articles by a conventional chlorinated hydrocarbon vapour degreaser, and the articles are left clean and dry and ready for the application of paint.

The phosphatable metals from which at least the surface of articles to be treated by the process of this invention must be made, are those known in the trade, e.g. iron, cast iron, steel, ferrous alloys and zinc and zinc alloys.

The aliphatic acids of the sorbitan esters, while normally straight chain, may be branched or substituted, and may be saturated or unsaturated; Examples are lauric, palmitic, stearic, oleic and linoleic acids.

The chlorinated hydrocarbons suitable for the process and composition of this invention are those known in the degreasing art, namely trichloroethylene, perchloroethylene and methyl chloroform.

It is known that it is possible to solubilize phosphoric acid in chlorinated hydrocarbons by using monoand dialkyl hydrogen phosphates as solubilizing agents. However, the amount of solubilization produced by such agents is quite small: for example, 10% by weight of octyl hydrogen phosphate will solubilize at the most 1% of the phosphoric acid. The solubilization produced by the sorbitan monoesters of the present invention is greater by a factor of ten. This gives the particular advantage that ten times the area of metal may be phosphated before the phosphoric acid requires replenishing. Furthermore, the process of the present invention is more rapid because of the greater amount of active phosphoric acid present.

It must be emphasized that the materials suitable for solubilizing phosphoric acid in chlorinated hydrocarbons for the purposes of this invention are limited to the sorbitan monesters described hereinbefore. Other related materials do not appear to be effective. Thus, for example, glyceryl monostearate and vinyl cyclohexene tetrol monopalrnitate are not efficient nor are the trisubstituted sorbitans such as sorbitan trioleate. The reason for the surprising and specific effects of the sorbitan monoesters is not known.

The phosphate coating produced on metal articles by the process and composition of this invention resembles very closely that produced by conventional aqueous systems, both in appearance and properties. The appearance is affected both by the temperature of the phosphating composition and the time of immersion therein or contact therewith. It may vary from a light grey to black as the immersion time is varied from one minute to fifteen minutes, but the process is not of course limited to these periods. Although an adequate coating is slowly produced at temperatures as low as 30 C., it is preferred to use a temperature between 50 C. and the boiling point of the composition, which will lie around 8791 C. when the chlorinated hydrocarbon is trichloroethylene, around 121125 C. when it is perchloroethylene and around 7073 C. when it is methyl chloroform. When a spray application is used the treatment is more rapid, and as little as 30 seconds contact time gives useful results.

It has further been discovered that a smoother and more even coating is produced on metallic articles if the composition of this invention also includes a soluble and compatible anionic surface active agent. Suitable agents arelthe alkyl benzene sulphonic acids, such as dodecyl benzene-sulphonic acid, but any anionic surfactant will serve which is soluble in the chlorinated hydrocarbon and is compatible, i.e., does not cause the formation of a precipitate in the presence of the sorbitan ester and phosphoric acid. Quantities of from 0.1 to 1.0%, by weight of the composition, of alkyl benzene sulphonic acid are suitable, but more or less may be used. For other agents the amounts are similar, but vary depending upon their molecular weight. The improvement achieved can be observed visually by inspection of the phosphate coating on the metal, and the inclusion of such agents is preferred in the process and composition of this invention.

The composition of this invention should be substantially anhydrous, however very minor quantities of water do not adversely affect the coating produced thereby nor do they form a separate phase. Thus the phosphoric acid used in the composition need not be completely anhydrous, but better results are obtained when a little phosphorus pentoxide is added to commercial phosphoric acid, either before addition to the chlorinated hydrocarbon containing the sorbitan monoester or after addition of the phosphoric acid to the chlorinated hydrocarbon.

The following examples areintended to illustrate the invention but are not to be construed as limiting in any manner thescope thereof.

Example 1 12.5 g. of sorbitan mono-stearate were dissolved in 250 cc. of trichloroethylene and 8.5 cc. of 100% phosphoric acid were dissolved in the cold solution at room temperature to produce a clear light yellow solution. The solution remained clear, homogeneous and stable on raising its temperature to the boiling point of the solution.

An automotive steel panel, which was partly covered with rust, grease, and other soil was immersed in the above boiling solution for a period of minutes. On removal from the solution, the panel was etched and had a uniform dull grey appearance. The panel was rinsed in boiling trichloroethylene and subsequently painted with a standard automotive primer and high bake enamel. The painted panel was examined for its resistance to blistering and its ability to resist underfilm corrosion at a break in the paint film. Its paint base characteristics were comparable to those obtained with phosphate coatings produced industrially using aqueous phosphating systems.

Example 2 A solution of g. of sorbitan monopalmitate in 200 cc. of trichloroethylene was prepared and4 g. of 100% phosphoric acidand 2 g. of dodecylbenzene sulphonic acid were dissolved in the cold solution. The solution remained stable and clear on boiling. Treatment of automotive steel panels by immersion in the boiling solution for seconds resulted in the formation of a light grey coating on the metal.

Treatment of automotive steel panels in this boiling solution for 15 minutes results in considerable etching of the surface and a uniform dark grey coating is produced.

Example 3 A solution of 10 g. of sorbitan monostearate in 200 cc. of perchloroethylene was prepared and 5 cc. of 100% phosphoric acid was added to the solution and the mixture heated to produce a clear solution. Treatment of automotive steel panels in this solution for 5 minutes at its boiling pointproducedlight, grey coatings.

Example 4 A solution of 16 g. of sorbitan monopalmitate was prepared in 200 cc. of trichloroethylene and 8 cc. of commercial concentrated phosphoric acid was added to the solution. The mixture was slightly cloudy but became completely clear on adding 6 g. of phosphorus pen toxide to the cold solution, while stirring.

Treatment of a steel panel in this clear solution at its boiling point for 30 seconds produced a light grey coating. The panel was rinsed in boiling trichloroethylene and was then painted with a standard primer and automotive enamel. The paint base characteristics of this coating were comparable with those obtained with phosphate coatings produced by aqueous treatments.

Example 5 6 grams of sorbitan monopalimitate were dissolved in 200 cc. of cold 1,1,l-trichloroethane (methyl chloroform) and 2 cc. of phosphoric acid were added to the cold solution and dissolved completely. The solution was heated to boilingand an automotive steel panel contaminated with oil and rust was immersed in the boiling solution for five minutes. The panel was subsequently rinsed in a trichloroethylene vapor degreaser. The treated panel was covered with a dull grey coating free from organic soil and rust.

What I claim is:

l. A substantially anhydrous composition suitable for cleaning and phosphating metal articles, which consists essentially of a chlorinated hydrocarbon degreasing solvent containing from about 1% to 10% by weight of at least one sorbitan monoester of an aliphatic acid having from 12 to 18 carbon atoms per molecule, and from one to six moles of phosphoric acid per mole of sorbitan monoester.

2. A composition as claimed in claim 1 wherein the chlorinated hydrocarbon is selected from the group consisting of trichloroethylene, perchloroethylene and math yl chloroform.

3. A composition as claimed in claim 1 wherein the sorbitan monoester is sorbitan monolaurate.

4. A composition as claimed in claim 1 wherein the sorbitan monoester is sorbitan monopalrnitate.

5. A composition as claimed in claim 1 wherein the sorbitan monoester is sorbitan monostearate.

6. A composition as claimed in claim 1 containing from about 0.1% to 1.0% by weight of an anionic sur-- face active agent soluble in the chlorinated hydrocarbon solvent and compatible with the phosphoric acid.

7. A composition as claimed in claim 1 containing from about 0.1% to 1.0% by weight of an alkyl benzene sulphonic acid.

8. A composition as claimed in claim 2 containing from about 0.1% to 1.0% by weight of dodecyl benzene sulphonic acid.

9. A process for cleaning and phosphating a metal article which comprises essentially coating the surface of the article with a substantially anhydrous composition consisting essentially of a chlorinated hydrocarbon degreasing solvent containing from about 1% to 10% by weight of at least one sorbitan monoester of an aliphatic acid having from 12 to 18 carbon atoms per molecule, and from one to six moles of phosphoric acid per mole of sorbitan monoester.

10. A process as claimed in claim 9 wherein the chlorinated hydrocarbon is selected from the group consisting of trichloroethylene, perchloroethylene and methyl chloroform.

11. A process as claimed in claim 9 wherein the sorbitan monoester is sorbitan monolaurate.

12. A process as claimed in claim 9 wherein the sorbitan monoester is sorbitan monopalmitate.

13. A process as claimed in claim 9 wherein the sorbitan monoester is sorbitan monostearate.

14. A- process as claimed'inclairn-9. wherein the com- 5 position contains from about 0.1% to 1.0% by weight of an anionic surface active agent soluble in the chlorinated hydrocarbon solvent and compatible with the phosphoric acid.

15. A process as claimed in claim 9 wherein the composition contains from about 0.1% to 1.0% of an alkyl benzene sulphonic acid.

16. A process as claimed in claim 10 wherein the composition contains from about 0.1% to 1.0% of dodecyl benzene sulphonic acid.

17. A process as claimed in claim 9 when conducted at a temperature between about 50 C. and the boiling point of the composition.

18. A process as claimed in claim 10 when conducted at a temperature between about 50 C. and the boiling point of the composition.

19. A substantially anhydrous composition suitable for cleaning and phosphating metal articles, which consists essentially of a chlorinated hydrocarbon degreasing solvent containing from about 1% to 10% by weight 20 of at least one sorbitan monoester of an aliphatic acid having from 12 to 18 carbon atoms per molecule, from one to six moles of commercial phosphoric acid per mole of sorbitan monoester, and phosphorous pentoxide in an amount approximately equivalent to the water in said commercial phosphoric acid.

20. A process for cleaning and phosphating a metal article which comprises coating the surface of the article with a substantially anhydrous composition consisting essentially of a chlorinated hydrocarbon degreasing solvent containing from about 1% to 10% by weight of at least one sorbitan monoester of an aliphatic acid having from 12 to 18 carbon atoms per molecule, from one to six moles of commercial phosphoric acid per mole of sorbitan monoester, and phosphorous pentoxide in an amount approximately equivalent to the water in said commercial phosphoric acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,396,776 Douty et a1. Mar. 19, 1946 2,789,070 Copelin Apr. 16, 1957 FOREIGN PATENTS 469,875 Canada Dec. 5, 1950 

1. A SUBSTANTIALLY ANHYDROUS COMPOSITION SUITABLE FOR CLEANING AND PHOSPHATING METAL ARTICLES, WHICH CONSISTS ESSENTIALLY OF A CHLORINATED HYDROCARBON DEGREASING SOLVENT CONTAINING FROM ABOUT 1% TO 10% BY WEIGHT OF AT LEAST ONE SORBITAN MONOESTER OF AN ALIPHATIC ACID HAVING FROM 12 TO 18 CARBON ATOMS PER MOLECULE, AND FROM ONE TO SIX MOLES OF PHOSPHORIC ACID PER MOLE OF SORBITAN MONOESTER. 